Years Ago, People Used Fountain Pens $\mathrm { f } ^ { - 1 }$

Essay

Years ago, people used fountain pens. The ink was very "wet" and so a blotter was used to absorb "wet" ink left
on the surface of the paper. Suppose you have a single sheet of graph paper and that you have just used your
fountain pen to graph the one-to-one function f. Explain how, if the ink is "wet", you could now obtain the
graph of f $\mathrm { f } ^ { - 1 }$ using only your sheet of graph paper. (Hint: Fold the sheet of graph paper.)